1. Field of the Invention
This invention is directed to operations involving the connection and disconnection of threaded tubular memebers, both at the surface in making and breaking connections with tongs and, in one particular aspect, in wellbore operations using wellbore tongs; to apparatus and methods for aligning wellbore tubulars; to power tongs used in making and breaking joints of tubular members such as pipe and wellbore casing and tubing; to parts thereof, including, but not limited to cam surface members elements; and methods of the use of these things.
2. Description of Related Art
Tongs are used to assist in the make-up and break-out of threaded tubular members. Certain operations during the drilling of oil and gas wells and the production of materials therefrom require the connection and disconnection of successive lengths of threaded tubulars such as pipe, casing, or tubing. Tools known as tongs are used to "make" and "break" such connections. Certain known power tongs have a body, a rotary rotatably mounted in said body and at least one active jaw with one, two or more cam rollers or followers, such a jaw (or jaws) on rotation of the rotary is cammed against a pipe in the rotary and grips it for rotation with the rotary. The camming action is typically generated by a cam member which is bolted to or machined as part of the rotary and is shaped so that the active jaw is cammed against the pipe on rotation of the rotary relative to the active jaw in one sense and will be released on rotation of the rotary relative to the active jaw in the opposite sense.
With known tongs, high torques are applied to tubulars due to combinations of factors such as thread sealing requirements, the presence of corrosion, the existence of distortion, and tolerances in pipe size and weight. Both in the "make" direction of rotation when a shoulder is suddenly encountered, and in the "break" direction at initial engagement of the tong and disengagement of the threads stresses may arise; e.g., with a power-driven tong, in excess of 50,000 foot-pounds of torque may be exerted, while die elements which may be relative small, or a jaw or jaws of the tong engage the pipe.
The grip mechanism of a tong translates a rotative input force into coplanar vector forces, acting chordally across the joint section. At the points of grip contact with the joint surface, these chordal forces are resolved into normal and tangential components relative to the joint contour and the rotative torque delivery capability of the tong system is a function of the normal component of the chordal vector multiplied by the coefficient of drag (friction) at the joint contact points of the grip elements. Grip elements are often provided with multiple serrations, or penetration features, to provide the interference contact needed at the joint surface for the development of a suitably high coefficient of drag (friction).
Torque delivery capability is a function of the normal force times the drag (friction) coefficient times the radius of the joint to be worked and the required magnitude of the normal force varies inversely with the coefficient of drag developed at the contact between the grip elements and the joint surface. Consequently, the distribution, balance and consistency of grip element energizing forces are critical factors in the design of a tong mechanism.
The prior art discloses a variety of mechanisms involving linkages, levers, wedges, and cams are in current use for the disposition and balance of the normal and tangential force components. Usually, grip elements, or dies, are disposed within carrier bodies, or jaws, which span a circumferential segment of the joint surface. These jaws are structured to accept the translated input chordal vector and deliver it to the joint surface in normal and tangential components.
FIG. 1H shows schematically a problem encountered with a prior art tong G having a jaw W with cam following rollers F. While one roller F may be maintained in contact with a corresponding cam surface of a rotary Y, the other roller F fails to contact a cam surface which can result in an unbalanced jaw/pipe contact. Another problem encountered with such systems occurs when both cam rollers are in contact with a cam surface, but jaw does not contact the pipe squarely. This is shown in FIG. 1H, and results in unbalanced contact of the jaw W with an outer surface of a pipe P, which can cause damage to the pipe P.
FIG. 2A shows a prior art tong N as disclosed in U.S. Pat. No. 4,404,876 which has cam surfaces B.sub.1, B.sub.2, B.sub.3, B.sub.4, B.sub.5, and B.sub.6 on a rotary D. Each of these cam surfaces is a part of a circle when viewed from above as in FIG. 2A. U.S. Pat. No. 4,404,876 discloses certain tong embodiments in which the cam angle does not exceed 51/2 degrees; others in which the cam angle is substantially 21/2 degrees; and others in which the cam angle is not substantially less than 1/2 degree. The cam angle for a tong, illustrated in FIG. 2B, is the angle between: (a) a line of action from the center of a rotary (which is also the center of the tubular being rotated) through a cam following member to a cam surface; and (b) a line through the cam following member normal to the cam surface at the point cam-following-member/cam-surface contact. The "cam angle" is defined in U.S. Pat. No. 4,404,876 as the angle formed by two lines originating at the point of contact between the cam and follower positioned when the dies are in contact with the pipe, by lines originating at the center of rotation of a rotary or partial ring of the tong and a point on a line perpendicular to the center line of a throat (for receiving a pipe section) and passing through the center of rotation and terminating at a point on the cam surface at which the cam follower or roller is positioned when dies or die carriers or jaws are in contact with a pipe section in the tong. Referring to a "cam angle" is a way of quantifying the ratio of tangential force and normal force applied through the cam from the rotary. The normal force at the jaw/pipe interface is equal to the above described normal force modified by the effect of any kinematic device between the jaw and the cam. Theoretically, it is preferred that an optimal cam angle be maintained for whatever position the cam follower or roller has on the entire length of the cam surface. In practice with various prior art circular-section cam surfaces, this is not achieved. FIGS. 1A-1G show a typical prior art power tong T that uses fixed or "centering" jaws J and a movable jaw M to grip pipe for tubular disconnecting and connecting operations. The jaws have gripping elements or dies D for engaging the pipe. An outer case C houses a powered rotary R to which fixed jaws J are mounted. A cam surface S of the rotary moves a movable (ACTIVE or MASTER) jaw M into (and away from) gripping contact with a tubular, e.g. pipe. The movable jaw M has one or two rollers L that move on the cam surface of the rotary. Each jaw has toothed gripping inserts to facilitate engagement with the surface of the tubular (see FIG. 1F). FIG. 1G shows the tong T in an "OPEN" position in which the tubular is not gripped. The cam surface S is defined by surfaces S.sub.1, S.sub.2, S.sub.3, S.sub.4, S.sub.5, and S.sub.6 on cam inserts I which are secured to the rotary R. Each of these surfaces is defined by part of a circle when viewed from above.
The prior art tong shown in FIG. 1A is a Weatherford Model 14.5-50 High Torque Tong. The brochure "New! Weatherford Model 14.5-50 High Torque Tong," (1991) and the manual entitled "Model 14.5-50 Hydraulic Power Tong Installation, Operation and Maintenance" (1993) are submitted herewith and incorporated herein fully by reference for all purposes. It is to be understood that the teachings of the present invention are applicable to any tong and any tong system that has one or more grippers or jaws and one or more cam surfaces and that the Model 14.5-50 tong is shown here for illustrative purposes and not by way of limitation of the scope of the present invention.
There has long been a need for a tong which applies a consistent force to a tubular to be rotated. There has long been a need for such a tong that efficiently rotates the pipe without damaging it and without slipping on it. There has long been a need for a tong with a jaw or jaws with two rollers in which the two rollers are maintained in contact with a tong cam surface.